New Boat Set - Electrical Recommendations Needed

[Mark P]

Looking at either a new NP 39 Pilothouse, or Helmsman 38E Pilothouse, with around 300 HP Cummins QSB 6.7 engine. These are questions from a newbie to trawling. We will be cruising the eastern seaboard, and the Loop at some point. Here goes, try not to laugh too much:

(1) When cruising at displacement speeds, can I run the AC, clothes washer, coffee maker etc, without the generator? I assume the engine charges the batteries while underway?
(2) Assuming I order the boat with a generator, if I anchor out, will the generator run all of the appliances, AC, lights on the boat?
(3) I assume shore power charges all batteries (including bow thruster?), and I can run all appliances, AC etc on shore power?
(4) Inverters - in reading the TF posts, these see to be problematic - do I need one? Not sure I understand what they do.

Any thoughts would be appreciated. Thank you.

 

[Comodave]

Looking at either a new NP 39 Pilothouse, or Helmsman 38E Pilothouse, with around 300 HP Cummins QSB 6.7 engine. These are questions from a newbie to trawling. We will be cruising the eastern seaboard, and the Loop at some point. Here goes, try not to laugh too much:

(1) When cruising at displacement speeds, can I run the AC, clothes washer, coffee maker etc, without the generator? I assume the engine charges the batteries while underway?
(2) Assuming I order the boat with a generator, if I anchor out, will the generator run all of the appliances, AC, lights on the boat?
(3) I assume shore power charges all batteries (including bow thruster?), and I can run all appliances, AC etc on shore power?
(4) Inverters - in reading the TF posts, these see to be problematic - do I need one? Not sure I understand what they do.

Any thoughts would be appreciated. Thank you.

1. The batteries will not run these unless you have an inverter since these are 120 volt appliances.
2. The generator will run all of these if you size it to run everything. The problem then is if you don’t run anything except say the battery charger, you are then underloading the generator. You have to make a decision as to what is reasonable for the genset to power at one time.
3. Usually all of the batteries will be charged by the charger(s). You can run whatever A/C you want when plugged into shore power up to the limit of your shore power service. If you have a 30 amp service you can usually run it up to about 23 to 24 amps continuously. If you have 2 30 amp inlets or a 50 amp inlet you will have more power to use.
4.inverters take 12 volts and turn it into 120 volts A/C. Yes there can be problems with them. You need a ABYC certified electrician to install one. You have to be aware of current draw from the battery bank since it can be very easy to use too much power from the bank when using an inverter. Inverters CAN run high draw appliances like A/C, but most battery banks will not support the current draw except for a very short time.

Good luck with your new boat. I recommend you sit down with a knowledgeable electrician and pick his/her brain before you make a decision. There are a lot of interactions with the new ground fault devices that are appearing on the docks.

 

[DavidM]

Answers below:

Looking at either a new NP 39 Pilothouse, or Helmsman 38E Pilothouse, with around 300 HP Cummins QSB 6.7 engine. These are questions from a newbie to trawling. We will be cruising the eastern seaboard, and the Loop at some point. Here goes, try not to laugh too much:

(1) When cruising at displacement speeds, can I run the AC, clothes washer, coffee maker etc, without the generator? No. The engine alternator won't put out enough DC power to run all of that stuff. Plus you would need a humongous inverter to do it. I assume the engine charges the batteries while underway? Yes but the standard alternator probably puts out less than 100 amps DC. 100 amps DC will only produce about 1KW AC with an inverter.

(2) Assuming I order the boat with a generator, if I anchor out, will the generator run all of the appliances, AC, lights on the boat? Yes, if it is big enough. For many boats the generator is sized so you can't run everything at once. You have to manage your loads, ie don't run the coffee maker while you wash clothes. If you size the generator to run everything, then it will be underloaded 95% of the time, which isn't good.

(3) I assume shore power charges all batteries (including bow thruster?), and I can run all appliances, AC etc on shore power? A typical marina 120/240V 50A shore power supply will do all of the above simultaneously in #1. That is more than 10 KW. Some marinas only have a single 120V 30A shore power outlet and that will not run them all simultaneously. Even if you pair two 30A 120V supplies that may not be able to run all of #1.

(4) Inverters - in reading the TF posts, these see to be problematic - do I need one? Not sure I understand what they do.

Good inverters such as Magnum, Victron, Mastervolt are not problematic. An inverter takes DC power from the batteries (see answer #1) and inverts it to 120 or even 240V AC to power big AC appliances. But it takes big batteries to power something for long, so it is usually for high load, short duration loads like a toaster, microwave, hair dryer and not an A/C. Most large inverters are combination shore power charger and inverter and automatically switch from shore power to inverter power if shore power is not available.

Any thoughts would be appreciated. Thank you.

If you are going to spend a half million $ on a new boat, I would hire a marine electrician and spend a few hours with him to understand what you want to power and with what and let him help you spec out your new boat.

A good starting point would be an 8KW generator feeding two 120V panel busses, one for the air conditioners and the other for everything else. Also install a 2-3 KW inverter/charger to feed the everything else buss. That will let you wash clothes and make coffee using inverter power while underway if you don't want to start the generator. You will also need a pretty big battery bank probably 400 AH unless you always run the generator at anchor. Also talk to the electrician about the need for a solar panel system.

Edit: Comodave and I said essentially the same thing. We must be right ;-).


David

 

[dhays]

Both of the above answers are excellent. In other words, even I can understand them. A couple points.

As was mentioned, you can run all your AC appliances when plugged into shore power IF your boats electrical service can support the amp draw AND the shore power can supply you with enough. This was mentioned above, but the same holds true for an inverter. You can only run as much AC from an inverter as the inverter (and your battery bank) can handle. The same is true (as was mentioned) for your genset.

The good news, is that you don’t have to figure out the design on your own. Both the Helmsman and North Pacific folks are used to building boats for the typical demands of east coast boaters. They can tell you what gensets their owners have found to be adequate for their needs.

Your questions are good however, You will get a basic understanding of how electrical systems are used.

 

[Mark P]

Guys. Appreciate all the comments! Very helpful as we research our boat. Thank you!

 

[Gordon J]

I run the washer (but not dryer off the inverter). I suspect a coffee pot with washer simultaneously would be too much. Our 12kw genny will run everything aboard simultaneously, to include 5 ACs.

Gordon